1. Field of the Invention
Present invention generally relates to marine vessels and particularly a hydrofoil assisted high speed hybrid hull featuring a slender central hull element and two or more side hull elements, the vessel basically operating as a hydrofoil stabilized super-slender monohull in the normal high speed mode.
2. Description of the Related Art
Among modern high speed vessels, the catamarans have over the two last decades gained a dominating market position over monohulls, particularly of size less than 100 meters. This type of vessel is characterized by its simplicity of operation, high stability and relatively high speed- and seakeeping capabilities, particularly in the speed regime of 30-35 knots. The marked, however, seems to continue putting increased demands to speed performance, and several catamarans making 45 knots, and exceptionally above 50 knots, have recently become a reality. Seakeeping performance has also become a major issue in modem high- speed marine transportation. These demands have resulted in larger propulsion power plant installations and the introduction of active motion damping systems, like T-foils located in the bow region and trim-tabs or interceptors located aft, for improvement of ride comfort. The introduction of T-foils, which basically are non permanent lift generating devices, however, is associated by a notable drag that reduces the speed with approximately 2-3 knots on a 40-45 knots catamaran.
Parallel with the increased speed demands on certain routes, most fast ferry operators are still reluctant to join this trend of development because of the associated sky-rocking fuel consumption. It is very likely that the catamaran technology, initially commercially developed during the early seventies, today have reached its optimum stage of development from a hydrodynamic point of view. Further reduction of drag is severely limited by the fact that the major drag component is related to hydrodynamic skin friction. To overcome this, either wetted surface area has to be reduced, or the skin friction has to be reduced by application of new technology, like air lubrication. Recognizing the lack of proven means to solve these technological challenges, it indicates that the catamaran concept, as we know it today, is no longer particularly suited to fully comply with the future marked needs in all respects. This view is supported by the increased attention concerning environmental issues paid by the public and authorities, which is likely to force through the development of novel concepts that performs better in this respect. Also the environment effects of the wave-making tendency of high speed crafts has become a growing regional concern.
The surface piecing hydrofoils were commercially developed in the mid fifties and produced in series by Rodriquez, Italy. As known, these are based on a monohull fitted with a forward- and aft-located surface piecing hydrofoil arrangement, which in the transverse section features a V-like shape of the foil span. Thus parts of the foil span protrude the waterline on both sides, and provide a transverse righting momentum when the craft heels causing the surface piercing foil span to be submerged. The hull is completely lifted out of the water at higher speed, being self stabilized in roll and pitch by the surface piecing hydrofoil arrangement. It is propelled by fully submerged propellers, mounted on inclined shafts. The advantages of this conceptual design over traditional monohulls of similar size were improved seakeeping and power-to-speed efficiency at service speed around 35 knots. The disadvantages were larger complexity, building costs, weight- and speed restriction. Therefore the design is generally limited to an overall length of around 40 m and maximum displacement of around 150 tons. The design became very popular as passenger ferries, and today there is still a large number of these operating around the world, particularly in previous Russian countries, Japan and the Mediterranean countries. According to the inventor""s opinion, there is probably no other high-speed concept that has transported the same amount of passengers so far. Compared to modern type high speed crafts, like catamarans and monohulls, the design has lost it""s popularity, and can no longer compete in terms of speed requirements and passenger comfort, though it still maintain an edge over these regarding speed-to-power efficiency.
On of the most significant steps in high-speed marine technology development came in the mid seventies when Boeing, USA, developed the Jetfoil. As the Rodriquez hydrofoils, the conceptual design is based on a monohull that is lifted clear of the waterline at higher speed, However, the foil system is based on the fully submerged type, which consists of a substantially plane fully submerged foil span supported by three vertical struts. As opposed to the surface-piercing hydrofoil, it is not self-stabilizing and therefore depends on controllable flaps integrated to the following edge of the foilspan. The primary foil is located aft extending to the full width of the craft, and provides the primary lift and roll stabilization. A lesser foil (T-foil) is located in the centerline forward and supported by a vertical strut. This provides a secondary lifting force as well as the required pitch controlling momentum. All foils can be tilted upward when the craft is in a fully displacement mode. The 27.4 m and 117 tons displacement Jetfoil design has a normal service speed in foil-born mode of around 45 knots. This design has the advantage of excellent seakeeping and high speed-to-power efficiency. The disadvantages, however, are high building costs, technical complexity, overall weight- and payload capacity restrictions.
In the early nineties, Kvaerner Fjellstrand and Westamarin, both Norway, developed the Foilcat concept. This is basically a catamaran fitted with a fully submerged foil system that lifts the craft clear of the waterline, and operates at a service speed of around 45 knots. The largest design is 35 m and has a maximum displacement of around 175 tons. It is described in Norwegian patent no. 175199. The design has basically the same advantages and disadvantages as the Jetfoils. This has limited its commercial acceptance. In order to reduce the large frictional resistance related to catamarans operating at speeds of around 45 knots, there is a resent trend towards developing foil assisted catamarans that is fitted with a fully submerged foil system for the purpose of lifting the hull partially out of the water. At the same time it is controlling the pitch, and to less degree roll and hive. Examples of these are U.S. Pat. No. 4,606,291 and U.S. Pat. No. 4,665,853. Since they are operating in a partial displacement mode, and as such still have two hulls submerged in the water, they are still left with a major frictional drag.
The trimaran design has gained increased reputation within the sailboat environment due to its high speed- and seakeeping capabilities. As known, the trimaran design consists of three fully submerged hull elements, including a long and narrow center hull and a pair of shorter outrigger hulls or sidehulls, integrated to the underside of a transverse bridging structure located midship or aft. However, this design is yet not brought into use in the high-speed ferry marked. Variations of this design are described in various patents and patent applications, like U.S. Pat. No. 4,348,972, U.S. Pat. No. 5,178,085, U.S. Pat. No. 5,529,009, JP 63130492, WO 93/07046, WO 94/20359, WO 97/10988 and EP455605. Some of these incorporate lifting devices in the form of T-foils fitted to the sidehulls and the center hull, for the purpose of damping roll and pitch motion. However, they all operate in a constant displacement mode with three hulls submerged.
A foil assisted hybrid marine vessel is described in U.S. Pat. No. 5,503,100. However, this particular invention seems to be impaired by a number of impracticable attributes that is likely to render the invention inapplicable as a high-speed craft. The reason for this being a combination of its complex hull geometry, unorthodox arrangement of the propulsion- and foil system, that ultimately will result in excessive overall weight and frictional drag.
The present novel design in a preferred version, is a hybrid between a monohull and trimaran. As known, the so-called Froude""s number, expressed by the formulae;
Fn=v/g*L
where, v=speed (m/s), g=gravitational acceleration, L=water line length (m)
plays an important role on a vessel""s wave-making resistance. Traditional trimarans featuring fully submerged side-hulls, tend to operate in a planing regime when the length of the sidehulls are short and the speed is sufficiently high. Due to stability requirements, implying a certain positive metacentric height (+GM), these tends to require a relatively large submergence of the side-hull in relation to its length, which generally leads to the risk of substantial increased wave-making drag at higher speed and Froude number.
The present invention is based upon a hybrid hull geometry consisting of a combination of an improved variation of the above mentioned trimarans and a monohulls, consisting of a deep slender central hull element and at least a pair of slender and shallow side hull elements being integrated to the vessel via a stiff deck construction connecting the side hull elements to the central hull element, and operating in two distinctly different modes, namely a hydrostatic stable lower speed mode, featuring a positive metacentric height (+GM) with the central hull element and at least one of the side hull elements submerged, and a hydrostatic unstable higher speed mode featuring a partly lifted, partly submerged central hull with a negative metacentric height (xe2x88x92GM) while the side hull elements are partly or entirely above the waterline, the transition from the one mode to the other being augmented by hydrodynamic lift-generating, roll-, heave and pitch controlling wings or hydrofoils, the vessel being characterized by a combination of following:
that the central hull element itself features a large water line length in relation to the water line width, and a large main deck width in relation to the water line width;
that the central hull element below it""s wet deck level has a transverse section as shown on FIG. 4a-d and 4e-m over a major portion of its length, eventually a combination of these;
that the side hull elements have a depth that is less, eventually substantially less that the depth of the central hull element, eventually of adjustable height, being positioned in the longitudinal direction such that a major portion lies aft of the vessels longitudinal center of gravity, or close to said center of gravity, and symmetrically about the vessels center line;
that at least one primary hydrodynamic wing- or hydrofoil arrangement is located between and below the central hull element and the side hull elements, integrated to these through vertical struts, eventually also to the in-between-laying wet deck construction through at least one vertical strut on each side of the vessel""s center line,
that at least one secondary hydrodynamic wing- or hydrofoil arrangement is located at an aft or forward position on the central hull element, eventually on both location, integrated to the vessel through at least one vertical strut for each set of hydrofoil arrangement, eventually also to the in-between-laying wet deck construction;
that the wings or hydrofoils are located such the center of hydrodynamic lift is located on or near the vessels longitudinal center of gravity;
that the hydrodynamic lift force generated by the hydrofoil arrangement at maximum speed is at least 20% of the lightest weight of the vessel
that the side hull elements consists of structurally integrated or independently fastened elements located below the wet deck and made of a stiff construction material or a flexible shock absorbing elastomeric material all over its length, or over a major portion of its length;
that the side hull elements contain flotation elements that are adjustable in the height all over the length of the side hull elements, or over a major portion of their length;
that the central hull element, preferably on larger vessels, is equipped with a water ballast tank, featuring a permanent opening located in the bottom plate of said hull at a distance forward of the said hull""s transom, for quick self- priming and draining, eventually equipped with means of remote controlled priming and draining.
In a preferred embodiment, the vessel is equipped with a fully submerged lift generating roll stabilizing and hive-damping primary hydrofoil arrangement located underneath and between the central hull element and the side hull elements, close to the vessels longitudinal center of gravity (LCG), and fixed to the central hull element, to the in-between-laying wet deck construction and the side hull elements by means of vertical, eventually also inclined, struts, and a secondary hydrodynamic lift generating and pitch controlling hydrofoil located aft, alternatively forward or both places, and fixed to the central hull element, eventually also to the in-between-laying wet deck construction, depending on the transverse span of the hydrofoil arrangement by means of vertical struts.
In another preferred version, particularly suited for vessels larger than 100 m, the vessel is equipped with two primary lift generating, roll stabilizing and pitch controlling high-aspect-ratio hydrofoils. Since vessels of this size normally will have full load displacement well in excess of 1000 metric tons, it may be desirable with respect to optimizing overall drag that the foil width is increased beyond the normal width of the vessel in order to provide a lift-to-displacement ratio in the range of 50% at 40-45 knots speed. Such an arrangement is shown in FIG. 8. Here, parts of the deck construction are extended transversely beyond the normal width of the vessel in order to facilitate support for the outer struts of the foils. These bridge constructions may also facilitate mooring as well as embarkation and disembarkation stations.
For larger versions, like approximately 200 m or larger, three primary lift generating foils may be feasible. In such a case their approximate location should be aft, forward and midship.
High speed hybrid marine vessel according to present invention is fitted with hydrodynamic lift-generating, roll-, heave and pitch controlling wings or hydrofoils, operating in two distinctly different modes, a hydrostatic stable lower speed mode, featuring a positive metacentric height (+GM), Keith the central hull element and at least one of the side hull elements submerged, and a hydrostatic unstable higher speed mode, featuring a negative metacentric height (xe2x88x92GM) with the slender central hull element partially lifted, partially submerged while the side hull elements are partly or entirely out of the water, while said vessel is being dynamically stabilized by the hydrofoil system, consisting of
a central hull element featuring an integrated stiff deck construction, that in the transverse direction protrudes beyond the width of the central hull element and where the lower surface of said deck construction, defined as the wet deck lays above the water line when the vessel is at rest at an intact condition, and at an increasing height above the mean water line when the vessel""s forward speed is substantially increased,
said vessel has a relation between the largest frame width above the waterline and the largest frame width of the central main element at a waterline representing any intact upright floating condition of at least 2,
said central hull element has a relation between the largest water line length and the largest water line width at any intact upright floating condition of at least 6,
said central hull element has a rectangular- or trapezoidal like shaped transverse section below the wet deck level at an aft location, gradually turning into a U-, V- and Y-shape closer to the bow, eventually a combination of these,
said vessel is provided with at least one set of side hull elements arranged such that one set consists of one side hull element located on each side of the vessel""s longitudinal centerline integrated below the wet deck, and featuring a depth that is less, eventually substantially less that the depth of the central hull element such that the ratio between the depth of the side hull elements and the depth of the central hull element is less than 0.7, the depth being measured from the lowest continuous deck running from the aft to the forward part of the vessel to the lowest part of the bottoms of said hull elements,
said side hull elements are in a preferred embodiment being located entirely or partly within the width envelope of above defined lowest continuous deck,
said side hull elements are in a preferred embodiment positioned such that a major portion of them lies aft of the vessels longitudinal center of gravity,
said side hull elements are in a preferred embodiment positioned such that the longitudinal location of their transom, lies aft of the transom of the central hull element,
said side hull elements are in a preferred embodiment located such that they are parallel to the vessel""s longitudinal center line, or at a minor inboard or outboard angle, and that said side hull elements are arranged symmetrically about the said vessel""s center line on both sides,
said side hull elements may, preferably on larger size vessels, be arranged one forward of the other on both sides in the longitudinal direction so that the vessels longitudinal center of gravity is located between the transom of the aft side hull elements and the bow of the forward side hull elements,
the wet deck is in the longitudinal direction at least extending from the upper and foremost part of the bow of the side hull elements to the transom of the central hull element, and features in the longitudinal direction an arc shape with the endpoints located at an higher level than any point elsewhere along the arc, or is in it""s entirety, or parts there off, horizontal, or in an angle to the horizontal plane with the aft end at a higher level than a point on the wet deck plane in between, eventually with a combination of an arc shaped middle part and angular oriented fore- and aft parts,
said wet deck is in the transverse direction horizontal or in an angular position, such that a point on said wet deck farther away form the vessel""s center line, lies at the same level, or on a higher level, as a point on said wet deck located closer to said center line.
In a preferred embodiment, said hybrid marine vessel further includes an arrangement constituting a set of fully submerged primary hydrodynamic wing or hydrofoil where the total transverse span of said hydrofoil arrangement corresponds at least to 50%, preferably close to 100%, of the largest overall width of the vessel, where said hydrofoil is located close to the vessel""s longitudinal center of gravity, or more precisely slightly forward of said point, fixed to the central hull element, the wet deck and the side hull elements, eventually parts of the wet deck or deck construction extending transversely beyond the said side hull elements, or to some of these structural elements dependent on the transverse span of said hydrofoil arrangement, by means of at least two vertical and/or inclined struts, that transfer the hydrodynamic lifting force to the vessel, normally an upwards directed force, and where it is provided at least one, preferably several, remotely controllable flap on each side of the vessel""s center line integrated to the trailing edge of the hydrofoil span, providing the required hydrodynamic stability by executing a controllable transverse righting momentum about the vessel""s centerline when the vessel moves forward at higher speed with the side-hull elements partly submerged or entirely above the mean waterline.
In a further preferred embodiment, said hybrid marine vessel includes an arrangement constituting at least one fully submerged secondary hydrodynamic wing or hydrofoil where the total transverse span of said hydrofoil arrangement is less than 50% of the largest overall width of the vessel, and where one set of said secondary hydrofoil arrangement is located substantially aft of the vessel""s longitudinal center of gravity, fixed to said central hull element and/or the wet deck, by means of at least one strut for each set of said hydrofoil that transfer the hydrodynamic force to the vessel, and where at least one remotely controllable flap for each set of said hydrofoil is integrated to the trailing edge, providing the required pitch regulating momentum about the vessels longitudinal pivoting center by executing a controllable longitudinal righting momentum when the vessel moves forward at higher speed.